So I had a "mic drop" moment cleaning my toilet. I've got hard
water that puts brown stains in the bottom front of my "newish" toilets in the siphon jet area (where no normal toilet brush will go) no matter how frequently I clean the toilets. I tried everything: a bottle brush, something similar to toothbrush (but more industrial), scotch-bright pads, nothing fully worked. I got frustrated and searched and found a product that was well-reviewed and realized it's only ingredient in it was citric acid. I have a huge bag of that and it was cheap. The instructions were 8oz in the tank & 8oz in the bowl (with residual water for both). Let sit and then flush ( I left it for an hour or so). My tank was clear from the the rust and the brown mineral deposit at the bottom of the toilet was gone. This isn't going to help anything that is more day-to-day
should be scrubbed away, but for mineral deposits it seems to work really well with zero work. The citric acid should only be added to plain water, so if you need to scrub with regular cleaner, do so first and flush that water away.